Mos capacitors structures for variable capacitor arrays and methods of forming the same

ABSTRACT

A capacitor structure is described. A capacitor structure including a substrate; a source/drain region formed in the substrate to form an active area having an active area width; and a plurality of gates formed above the substrate. The source/drain region having a reflection symmetry. Each of the plurality of gates having a gate width. The gate width is configured to be less than said active area width. And, the plurality of gates are formed to have reflection symmetry.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/140,319 filed on Mar. 30, 2015, which is hereby incorporated by reference in its entirety.

FIELD

Embodiments of the invention relate to electronic systems and, in particular, to variable capacitors.

BACKGROUND

A wireless device such as a smart phone, tablet, or laptop computer can communicate over multiple frequency bands using one or more common or shared antennas. A desire to transmit at wider bandwidth and/or over different communications networks has increased a demand for the number of bands that a wireless device can communicate over. For example, a wireless device may be specified to operate using one or more of a variety of communications standards including, for example, GSM/EDGE, IMT-2000 (3G), 4G, Long Term Evolution (LTE), Advanced LTE, IEEE 802.11 (Wi-Fi), Mobile WiMAX, Near Field Communication (NFC), Global Positioning System (GPS), GLONASS, Galileo, Bluetooth, and the like. Proprietary standards can also be applicable. The complexities of multi-band communication can be further exacerbated in configurations in which the wireless device is specified to use carrier aggregation.

SUMMARY

A capacitor structure is described. A capacitor structure including a substrate; a source/drain region formed in the substrate to form an active area having an active area width; and a plurality of gates formed above the substrate. The source/drain region having a reflection symmetry. Each of the plurality of gates having a gate width. The gate width is configured to be less than said active area width. And, the plurality of gates are formed to have reflection symmetry.

Other features and advantages of embodiments of the present invention will be apparent from the accompanying drawings and from the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:

FIG. 1 is a schematic plan view of one embodiment of a metal oxide semiconductor (MOS) capacitor structure for a variable capacitor array according to an embodiment;

FIG. 2A is a schematic diagram of one embodiment of a radio frequency (RF) system;

FIG. 2B is a schematic diagram of another embodiment of an RF system;

FIG. 2C is a schematic diagram of another embodiment of an RF system;

FIG. 3 illustrates a schematic diagram of a programmable filter according to one embodiment;

FIG. 4A illustrates a schematic diagram of one embodiment of an RF signal processing circuit according to an embodiment;

FIG. 4B illustrates a schematic diagram of another embodiment of an RF signal processing circuit according to an embodiment;

FIG. 5 illustrates a schematic diagram of an IC according to another embodiment;

FIGS. 6A and 6B illustrate graphs of two examples of capacitance versus bias voltage;

FIG. 7 illustrates a schematic diagram of an IC according to another embodiment;

FIG. 8 illustrates a schematic diagram of an IC according to another embodiment;

FIG. 9A illustrates a circuit diagram of a variable capacitor cell according to one embodiment;

FIG. 9B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 10A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 10B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 11A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 11B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 12A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 12B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 13A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 13B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 14A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 14B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 15A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 15B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 16A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 16B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 17A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 17B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 18A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 18B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 19A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 19B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 20A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 20B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 21A illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 21B illustrates a circuit diagram of a variable capacitor cell according to another embodiment;

FIG. 22 is a schematic diagram of a cross section of an IC according to one embodiment;

FIG. 23A is a cross section of a MOS capacitor according to one embodiment; and

FIG. 23B is a cross section of a MOS capacitor according to another embodiment.

DETAILED DESCRIPTION

Disclosed herein are MOS capacitor structures for variable capacitor arrays.

In certain embodiments, the MOS capacitor structures can be fabricated using silicon on insulator (SOI) processes. Thus, the MOS capacitor structures can be included in an integrated circuit (IC) that is in an SOI substrate. For example, the integrated circuit can include a support substrate, an insulator layer (for example, a buried oxide layer) over the support substrate, and a device layer over the insulator layer. The MOS capacitors can include source and drain diffusion regions that are formed in the device layer.

MOS capacitors can be included in variable capacitor array that includes a plurality of MOS variable capacitor cells. In certain configurations, the plurality of MOS variable capacitor cells can include pairs of MOS capacitors that are implemented in anti-series and/or anti-parallel configurations. Examples of MOS variable capacitor arrays can be as described in Ser. No. 14/559,783 and in U.S. Patent Publication No. 2014/0354348, now U.S. Pat. No. 9,086,709, each of which are hereby expressly incorporated by reference herein in their entirety.

FIG. 1 is a schematic plan view of one embodiment of a metal oxide semiconductor (MOS) capacitor structure for a variable capacitor array.

The illustrated MOS capacitor structure 1000 includes gates 1040 that do not extend across the full source/drain diffusion region 1020. Such a device can be referred to herein as a flow device. Configuring the MOS capacitor structure 1000 in this manner can provide a resistive DC path through source/drain diffusion which can be used to bias the device.

The one or more source/drain regions 1020 are formed in a substrate, such as an SOI substrate, using doping techniques including those known in the art. The plurality of gates 1040 are formed above the substrate, using techniques including those known in the art, such that a finger spacing 1090 is maintained between each gate 1040 of the plurality of gates 1040. The plurality of gates 1040 are formed above the source/drain region 1020 to form a channel 1100 within the active area width 1050. The plurality of gates 1040 are interconnected using a metal interconnect 1080 and one or more contacts 1060.

Further, for various embodiments, a plurality of gates 1040 are formed above the substrate. For example, the plurality of gates 1040 a are formed of polysilicon formed above the substrate on an oxide layer using techniques including those known in the art. Such a plurality of gates 1040 are formed having a gate/finger width 1030 such that the gate width 1030 is configured to be less than the active area width 1050. Further, the source/drain (S/D) regions 1020 may be interconnected using a metal interconnect. The metal interconnects are formed using techniques including those known in the art. Thus, the MOS capacitor structure 1000 includes a separation or gap 1070 between an end of the gate and an edge of the source/drain diffusion region 1020.

The MOS capacitor structure 1000 can be biased using a relatively small number of contacts. In certain configurations, the S/D region 1020 is contacted using contacts 1060. The contacts 1060 are formed using techniques including those known in the art.

Certain MOS capacitor devices can be biased using a set of contacts for each FET channel area (E). Including a set of contacts for each FET channel area can increase finger-to-finger spacing (I) and an overall active area height (D) for a given (width (W)*length (L)*number of fingers) FET channel area.

In contrast, the illustrated MOS capacitor structure 1000 includes gates 1040 that do not extend the full source/drain diffusion width (active area width) 1050. This advantageously decreases active area height (D) 1093 decreases the length of the input/output routes (H) 1090, thereby decreasing the series resistance of these routes and increasing Q-factor.

The MOS variable capacitor arrays implemented in accordance with the teachings herein can exhibit high densities.

Substrate coupling due to routing over the substrate can degrade Q-factor. Such substrate coupling can be proportional to area of the circuit element and/or distance of the circuit element from the substrate.

In certain implementations, area reduction is in favor of active area over polysilicon area. Active area can have a poorer substrate performance, relative to polysilicon area.

In one embodiment, the gate and/or source/drain regions of the variable capacitor structure exhibits reflectional symmetry. For various embodiments, a source/drain region 1020 is formed to have a reflectional symmetry along one or more lines of symmetry. Further, the plurality of gates 1040 formed above the source/drain region 1020 are formed to have a reflectional symmetry along one or more lines of symmetry.

The MOS capacitor structure of FIG. 1 can represent a portion of a larger variable capacitor array.

Additionally, the MOS capacitor structure can be adapted to include more or fewer gate and active regions and/or different configurations of metallization and contacts to aid in implementing a variable capacitor array with a desired overall performance characteristic. For instance, the MOS capacitor structure can be scaled, replicated, and/or mirrored to implement a variable capacitor array including a desired number of and/or configuration of MOS variable capacitor cells.

FIG. 2A is a schematic diagram of one embodiment of a radio frequency (RF) system 10. The RF system 10 includes a programmable duplexer 1, an antenna 2, a receive terminal RX, and a transmit terminal TX. The RF system 10 can represent a portion of a wireless device, such as a smart phone. Accordingly, although not illustrated in FIG. 2A for clarity, the RF system 10 can include additional components and/or circuitry.

As shown in FIG. 2A, the programmable duplexer 1 includes a first programmable filter 3 and a second programmable filter 4. The first programmable filter 3 includes an input electrically connected to the antenna 2 and an output electrically connected to the receive terminal RX. The first programmable filter 3 further includes a first variable capacitor array 5, which can be used to control a filtering characteristic of the first programmable filter 3, such as the location in frequency of a passband. The second programmable filter 4 includes an input electrically connected to the transmit terminal TX and an output electrically connected to the antenna 2. The second programmable filter 4 further includes a second variable capacitor array 6, which can be used to control a filtering characteristic of the second programmable filter 4.

A wireless device such as a smart phone, tablet, or laptop computer can communicate over multiple frequency bands using one or more common or shared antennas. A desire to transmit at wider bandwidth and/or over different communications networks has increased a demand for the number of bands that a wireless device can communicate over. For example, a wireless device may be specified to operate using one or more of a variety of communications standards including, for example, GSM/EDGE, IMT-2000 (3G), 4G, Long Term Evolution (LTE), Advanced LTE, IEEE 802.11 (Wi-Fi), Mobile WiMAX, Near Field Communication (NFC), Global Positioning System (GPS), GLONASS, Galileo, Bluetooth, and the like. Proprietary standards can also be applicable. The complexities of multi-band communication can be further exacerbated in configurations in which the wireless device is specified to use carrier aggregation.

Certain conventional wireless devices can include a multi-throw switch and a duplexer associated with each of the frequency bands, and the multi-throw switch can be used to selectively couple an antenna to a duplexer associated with a particular band. The duplexers can provide band filtering using, for example, passive filtering structures, such as a surface acoustic wave (SAW) filters and/or thin film bulk acoustic resonators (FBARs). The multi-throw switch can be used to electrically couple the antenna to a duplexer associated with a frequency band that the wireless device is transmitting and/or receiving over at a particular time instance.

In the illustrated configuration, the programmable duplexer 1 can be configured to filter a particular frequency band by programming the first and second programmable filters 3, 4 using a control signal CNTL. For example, in certain embodiments, the capacitance value of the first variable capacitor array 5 can be controlled using the control signal CNTL to control a frequency location of a passband of the first programmable filter 3, and the capacitance value of the second variable capacitor array 6 can be controlled using the control signal CNTL to control a frequency location of a passband of the second programmable filter 4.

Accordingly, the programmable duplexer 1 can be used to provide the RF system 10 with multi-band capability, while avoiding a need for using a multi-throw switch and a duplexer for each frequency band. Including the programmable duplexer 1 in the RF system 10 can reduce insertion loss in transmit and/or receive paths by eliminating a need for a multi throw switch. Furthermore, the programmable duplexer 1 can have smaller area relative to a configuration including a multi-throw switch and multiple duplexers. Thus, a wireless device that includes the programmable duplexer 1 can have a smaller form factor and/or lower cost.

In the illustrated configuration, the capacitance values of the first and second variable capacitor arrays 5, 6 can be controlled using the control signal CNTL. In one embodiment, the control signal CNTL is received by the programmable duplexer 1 over an interface, such as a serial peripheral interface (SPI) or Mobile Industry Processor Interface radio frequency front end (MIPI RFFE) interface. Although two examples of interfaces have been provided, other interfaces can be used. Although FIG. 2A illustrates the first and second variable capacitor arrays 5, 6 as receiving a common control signal CNTL, other configurations are possible, such as implementations in which the first and second variable capacitor arrays 5, 6 are controlled using separate control signals.

The first variable capacitor array 5 and/or the second variable capacitor structure 6 can be implemented using one or more embodiments of variable capacitor arrays described herein. Thus, the first and second variable capacitor arrays 5, 6 can include metal oxide semiconductor (MOS) capacitors, which can offer enhanced performance over certain other tunable capacitance structures. For instance, certain microelectromechanical systems (MEMS) capacitors can exhibit low Q-factor, poor reliability, and/or limited tuning range. Additionally, other approaches such as coupled resonators can suffer from large size and/or cost, and thus can be unsuitable for certain applications, including smart phones.

FIG. 2B is a schematic diagram of another embodiment of an RF system 2000 that includes an RF circuit 1500. The RF circuit 1500 includes a tunable input matching network 2100 electrically connected to an RF input IN and a tunable output matching network 2200 electrically connected to an RF output OUT. As shown in FIG. 2B, the tunable input matching network 2100 and the tunable output matching network 2200 include first and second variable capacitor arrays 5, 6, respectively.

The first variable capacitor array 5 receives the control signal CNTL, which can be used to control the first variable capacitor array's capacitance. The capacitance of the first variable capacitor array 5 can be used to control, for example, an input impedance of the RF circuit 1500 and/or to control a ratio of impedance transformation provided by the tunable input matching network 2100. Additionally, the capacitance of the second variable capacitor array 6 can be controlled by the control signal CNTL, thereby controlling, for example, an output impedance of the RF circuit 1500 and/or a ratio of impedance transformation provided by the tunable output matching network 2200.

Including the tunable input matching network 2100 and the tunable output matching network 2200 can enhance performance in a variety of ways, such as improving performance under varying voltage standing wave ratio (VSWR). The first and second variable capacitor arrays 5, 6 can be implemented in accordance with the teachings herein to provide high RF voltage handling capabilities, high Q-factor, low insertion loss, and/or high linearity.

FIG. 2C is a schematic diagram of another embodiment of an RF system 3000 that includes an antenna tuning circuit 3100 and an antenna 2. The antenna tuning circuit 3100 is electrically connected between an RF terminal IN and the antenna 2.

As shown in FIG. 2C, the antenna tuning circuit 31 includes the variable capacitor array 5, which can be controlled using the control signal CNTL. The capacitance of the variable capacitor array 5 can be used, for example, to control an impedance transformation provided by the antenna tuning circuit 3100 and/or a standing wave ratio on the RF terminal IN.

Although the RF systems of FIGS. 2A-2C illustrate various examples of electronic systems that can include one or more variable capacitor arrays, the variable capacitor arrays described herein can be used in other electronic systems. For example, variable capacitor arrays can be used in wide range of RF electronics, including, for example, programmable filters, programmable resonators, programmable antenna tuners, programmable impedance matching networks, programmable phase shifters, and/or programmable duplexers.

FIG. 3 is a schematic diagram of a programmable filter 20 according to one embodiment. The programmable filter 20 includes an input impedance transformer 11, a splitter transformer 12, an RF signal processing circuit 13, a combiner transformer 14, and an output impedance transformer 15. The programmable filter 20 further includes an RF input IN and an RF output OUT. For various embodiments, the programmable filter 20 is configured as a tunable notch filter including those described herein.

The input impedance transformer 11 can receive an RF input signal on the RF input IN, and can generate an impedance transformed signal 21. The input impedance transformer 11 can provide an impedance transformation from input to output. For example, in one embodiment, the input impedance transformer 11 transforms an input impedance of about 50Ω to an output impedance of about R_(L), where R_(L) is less than 50Ω, for example, 8Ω.

Transforming the input impedance of the programmable filter 20 in this manner can result in the impedance transformed signal 21 having a smaller voltage level relative to a voltage level of the RF input signal received at the RF input IN. For example, when the programmable filter 20 has an input impedance of about 50Ω, the voltage level of the impedance transformed signal 21 can be smaller than the voltage level of the RF input signal by a factor of about √{square root over (50/R_(L))}.

The splitter transformer 12 can receive the impedance transformed signal 21 from the input impedance transformer 11, and can generate N split signals, where N is an integer greater than or equal to 2. In the illustrated configuration, the splitter transformer 12 generates a first split signal 22 a, a second split signal 22 b, and a third split signal 22 c. Although an example with N=3 has been illustrated, the principles and advantages disclosed herein are applicable to a broad range of values for the integer N, including 2, 3, 4, 5, or 6 or more.

Splitting the impedance transformed signal 21 into N split signals can further decrease a voltage level of the RF input signal by a factor of N. Including the splitter transformer 12 can also reduce the impedance by a factor of N. For example, when the output impedance of the input impedance transformer 11 has a value of R_(L), the output impedance of each output of the splitter transformer 12 can have a value of R_(L)/N.

As shown in FIG. 3, the RF signal processing circuit 13 can receive the first, second, and third split signals 22 a-22 c, and can generate first, second, and third processed RF signals 23 a-23 c, respectively. As illustrated in FIG. 3, the RF signal processing circuit 13 includes variable capacitor arrays 16, which can be used to control a filtering characteristic of the RF signal processing circuit 13. The RF signal processing circuit 13 further receives a control signal CNTL, which can be used to control the capacitances of the variable capacitor arrays 16.

The illustrated RF signal processing circuit 13 can be used to process the split signals 22 a-22 c generated by the splitter transformer 12 to generate the processed signals 23 a-23 c, respectively. In certain configurations, the RF signal processing circuit 13 can include substantially identical circuitry in the signal paths between the RF signal processing circuit's inputs and outputs.

The combiner transformer 14 receives the processed signals 23 a-23 c, which the combiner transformer 14 can combine to generate a combined signal 24. The combiner transformer 14 can also provide an impedance transformation. For example, in a configuration in which each output of the RF signal processing circuit 13 has an output impedance of about R_(L)/N, the combiner transformer 14 can have an output impedance of about R_(L).

The output impedance transformer 15 receives the combined signal 24 from the combiner transformer 14, and generates the RF output signal on the RF output OUT. In certain configurations, the combiner transformer 14 can have an output impedance R_(L) that is less than 50Ω, and the output impedance transformer 15 can be used to provide the RF output signal at an output impedance of about 50Ω.

The illustrated programmable filter 20 provides filtering using the RF signal processing circuit 13, which processes the split signals 22 a-22 c at lower impedance relative to the programmable filter's input impedance. Thereafter, the processed signals 23 a-23 c are combined and transformed up in impedance. For example, in one embodiment, the programmable filter's output impedance is about equal to the programmable filter's input impedance.

Configuring the programmable filter 20 to process an RF input signal in this manner can increase the programmable filter's voltage handling capability. For example, when the programmable filter 20 has an input impedance of about 50Ω, the voltage level of the RF input signal can be decreased by a factor of about N√{square root over (50/R_(L))} before it is provided to the RF signal processing circuit 13, which may include circuitry that is sensitive to high voltage conditions. Accordingly, the illustrated programmable filter 20 can be used to process high voltage RF input signals and/or can have enhanced robustness to variations in voltage standing wave ratio (VWSR).

Furthermore, configuring the programmable filter 20 to process the RF signal at lower impedance can enhance the programmable filter's linearity. In one embodiment, the illustrated configuration can reduce the third-order inter-modulation distortion (IMD3) by a factor of about 40 log₁₀ N√{square root over (50/R_(L))} relative to a configuration in which an RF input signal is provided directly to an RF signal processing circuit without impedance transformation or splitting. In one illustrative example, N can be selected to be equal to 8 and R_(L) can be selected to be about equal to about 8Ω, and the programmable filter can provide a linearity improvement of about 52 dB. However, other configurations are possible.

FIG. 4A is a schematic diagram of one embodiment of an RF signal processing circuit 30. The RF signal processing circuit 30 includes a first inductor-capacitor (LC) circuit 31 a, a second LC circuit 31 b, a third LC circuit 31 c, a fourth LC circuit 31 d, a fifth LC circuit 31 e, a sixth LC circuit 31 f, a seventh LC circuit 31 g, an eighth LC circuit 31 h, and a ninth LC circuit 31 i. The RF signal processing circuit 30 illustrates one embodiment of the RF signal processing circuit 13 of FIG. 3.

As shown in FIG. 4A, the first, second, and third LC circuits 31 a-31 c are arranged in a cascade between a first RF input I₁ and a first RF output O₁. Additionally, the fourth, fifth, and sixth LC circuits 31 d-31 f are arranged in a cascade between a second RF input I₂ and a second RF output O₂. Furthermore, the seventh, eighth, and ninth LC circuits 31 g-31 i are arranged in a cascade between a third RF input I₃ and a third RF output O₃.

Although FIG. 4A illustrates a configuration including three RF inputs and three RF outputs, the RF signal processing circuit 30 can be adapted to include more or fewer inputs and outputs.

The RF signal processing circuit 30 can be used to process RF input signals received on the first to third RF inputs I₁-I₃ to generate RF output signals on the first to third RF outputs O₁-O₃. As shown in FIG. 4A, the RF signal processing circuit 30 receives a control signal CNTL, which can be used to control one or more variable capacitances associated with the first to ninth LC circuits 31 a-31 i. By controlling the LC circuits' capacitances, the control signal CNTL can be used to tune a frequency response of the RF signal processing circuit 30.

In one embodiment, the RF signal processing circuit 30 is configured to operate as a notch filter using techniques including those known in the art, and the control signal CNTL can be used to control a location in frequency of the notch filter's stopband. However, other configurations are possible.

Although FIG. 4A illustrates a configuration including three LC circuits arranged in a cascade between each input and output, more or fewer LC circuits and/or other processing circuitry can be included.

Cascading LC circuits can increase a voltage handling capability of an RF signal processing circuit by limiting a voltage drop across individual circuit components of the LC circuits. For example, in certain implementations, the LC circuits 31 a-31 i are implemented using MOS capacitors, which can be damaged by large gate-to-drain and/or gate-to-source voltages. By arranging two or more LC circuits in a cascade, a voltage drop across the MOS capacitors during operation can be increased relative to a configuration including a single LC circuit between a particular input and output.

The RF signal processing circuit 30 illustrates one embodiment of the RF signal processing circuit 13 of FIG. 4A. For example, in certain configurations, the first to third input RF inputs I₁-I₃ can receive the first to third RF split signals 22 a-22 c, respectively, and the first to third RF outputs O₁-O₃ can generate the first to third processed signals 23 a-23 c, respectively.

The RF signal processing circuit 30 includes a first signal path between the first RF input I₁ and the first RF output O₁, a second signal path between the second RF input I₂ and the second RF output O₂, and a third signal path between the third RF input I₃ and the third RF output O₃. In certain configurations, one or more electrical connections can be provided between corresponding positions along the first to third signals paths. For example, in certain implementations, the RF signal processing circuit 30 is used to process substantially identical RF input signals received on the first to third RF inputs I₁-I₃, respectively, to generate substantially identical RF output signals on the first to third RF outputs O₁-O₃. In such configurations, electrical connections can be provided along corresponding positions of signal paths, since the corresponding positions should have substantially the same voltage level. Examples of such electrical connections are illustrated in FIG. 4A with dashed lines.

FIG. 4B is a schematic diagram of another embodiment of an RF signal processing circuit 40. The RF signal processing circuit 40 includes a first LC circuit 41 a, a second LC circuit 41 b, a third LC circuit 41 c, a fourth LC circuit 41 d, a fifth LC circuit 41 e, a sixth LC circuit 41 f, a seventh LC circuit 41 g, an eighth LC circuit 41 h, and a ninth LC circuit 41 i.

The first to ninth LC circuits 41 a-41 i each include an input and an output. The first, second, and third LC circuits 41 a-41 c are arranged in a cascade between the first RF input I1 and the first RF output O1. Additionally, the fourth, fifth, and sixth LC circuits 41 d-41 f are arranged in a cascade between the second RF input I2 and second RF output O2. Furthermore, the seventh, eighth, and ninth LC circuits are arranged in a cascade between the third RF input I3 and the third RF output O3.

The first LC circuit 41 a includes a first variable capacitor 43 a, a second variable capacitor 44 a, a first inductor 45 a, a second inductor 46 a, and a third inductor 47 a. The first variable capacitor 43 a includes a first end electrically connected to the input of first LC circuit 41 a, and a second end electrically connected to a first end of the first inductor 45 a. The first inductor 45 a further includes a second end electrically connected to a first end of the second inductor 46 a and to a first end of the third inductor 47 a. The second variable capacitor 44 a includes a first end electrically connected to a second end of the second inductor 46 a and a second end electrically connected to a first voltage V1, which can be, for example, a ground or power low supply. The third inductor 47 a further includes a second end electrically connected to an output of the first LC circuit 41 a.

The second to ninth LC circuits 41 b-41 i include first variable capacitors 43 b 43 i, second variable capacitors 44 b-44 i, first inductors 45 b-45 i, second inductors 46 b 46 i, and third inductors 47 b-47 i, respectively. Additional details of the second to ninth LC circuits 41 b 41 i can be similar to those described above with respect to the first LC circuit 41 a.

The control signal CNTL can be used to control variable capacitances of the variable capacitors of the first to ninth LC circuits 41 a 41 i, thereby controlling a passband of the RF signal processing circuit 40. In certain implementations, an inductance of the first to ninth LC circuits 41 a 41 i is substantially fixed or constant.

In certain configurations, all or part of the variable capacitors of an RF signal processing circuit are implemented using variable capacitor arrays fabricated on one or more integrated circuits. For example, as shown in FIG. 4B, in one embodiment, the first variable capacitor 43 a, the fourth variable capacitor 43 d, and the seventh variable capacitor 44 g are fabricated as three variable capacitor arrays on a first IC 50. Additionally, the other variable capacitors shown in FIG. 4B can be fabricated as variable capacitor arrays on the first IC 50 or on one or more additional ICs. Although one example of implementing variable capacitors as variable capacitor arrays has been described, other configurations are possible.

In one embodiment, the control signal CNTL is received over an interface, such as a serial peripheral interface (SPI) or Mobile Industry Processor Interface radio frequency front end (MIPI RFFE) interface.

As described above, various embodiments of a tunable phasing network include one or more metal oxide semiconductor (MOS) variable capacitor arrays. For various embodiments, a variable capacitor array includes a plurality of variable capacitor cells electrically connected in parallel. Each of the variable capacitor cells can include a cascade of two or more pairs of anti-series metal oxide semiconductor (MOS) capacitors between an RF input and an RF output. The pairs of anti-series MOS capacitors include a first MOS capacitor and a second MOS capacitor electrically connected in anti-series. A bias voltage generation circuit generates bias voltages for biasing the MOS capacitors of the MOS variable capacitor cells.

A MOS capacitor, according to various embodiments, includes a gate that operates as an anode, and a source and drain that are electrically connected to one another and operate as a cathode. Additionally, a DC bias voltage between the MOS capacitor's anode and cathode can be used to control the MOS capacitor's capacitance. In certain configurations, two or more pairs of anti-series MOS capacitors are cascaded to operate as a variable capacitor cell. As used herein, a pair of MOS capacitors can be electrically connected in anti-series or inverse series when the pair of MOS capacitors is electrically connected in series with the first and second MOS capacitors' anodes electrically connected to one another or with the first and second MOS capacitors' cathodes electrically connected to one another.

The variable capacitor arrays disclosed herein can exhibit high RF signal handling and/or power handling capabilities. For example, including two or more pairs of anti-series MOS capacitors in a cascade can facilitate handling of RF signals with relatively large peak-to-peak voltage swings by distributing the RF signal voltage across multiple MOS capacitors. Thus, the variable capacitor array can handle RF signals of large voltage amplitude and/or high power without overvoltage conditions that may otherwise cause transistor damage, such as gate oxide punch through.

In certain configurations, the bias voltage generation circuit can bias the MOS capacitors of a particular variable capacitor cell at a voltage level selected from a discrete number of two or more bias voltage levels associated with high linearity. Thus, rather than biasing the MOS capacitors at a bias voltage level selected from a continuous tuning voltage range, the bias voltage generation circuit generates the MOS capacitors' bias voltages by selecting a particular cell's bias voltage level from a discrete set of bias voltage levels associated with high linearity. In one embodiment, the bias voltage generation circuit biases a particular MOS capacitor either at a first bias voltage level associated with an accumulation mode of the MOS capacitor or at a second bias voltage level associated an inversion mode of the MOS capacitor.

As used herein and as persons having ordinary skill in the art will appreciate, the terms MOS capacitors refer to any types of capacitors made from transistors with insulated gates. These MOS capacitors can have gates made from metals, such as aluminum, and dielectric regions made out of silicon oxide. However, these MOS capacitors can alternatively have gates made out of materials that are not metals, such as poly silicon, and can have dielectric regions implemented not just with silicon oxide, but with other dielectrics, such as high-k dielectrics. In certain embodiments, the MOS capacitors are implemented using fabricated using silicon on insulator (SOI) processes. For example, an integrated circuit can include a support substrate, a buried oxide (BOX) layer over the support substrate, and a device layer over the BOX layer, and the MOS capacitors can be fabricated in the device layer.

In certain embodiments, a variable capacitor array omits any switches in the signal path between the variable capacitor array's RF input and RF output. Switches can introduce insertion loss, degrade Q-factor, and/or decrease linearity. Thus, rather than providing capacitance tuning by opening and closing switches to set a number of active capacitors from a capacitor bank, capacitance tuning can be provided by biasing MOS capacitors of the variable capacitor cells at different bias voltage levels to provide a desired overall capacitance of the variable capacitor array. In certain configurations, the variable capacitor cells of the variable capacitor array can have the same or different weights or sizes, and the variable capacitor array's overall capacitance is based on a linear combination of the capacitances of the variable capacitor cells.

The variable capacitor arrays herein can have high RF voltage handling capability, while having a relatively small size, a relatively high Q-factor, a relatively high linearity, and/or a relatively low insertion loss. Furthermore, in certain implementations, a variable capacitor array can provide sufficient tuning range to provide filtering across a variety of different frequency bands. Accordingly, the variable capacitor array may be used to provide frequency tuning in a wide range of RF electronics, including, for example, programmable filters, programmable resonators, programmable antenna tuners, programmable impedance matching networks, programmable phase shifters, and/or programmable duplexers.

A wireless device such as a smart phone, tablet, or laptop computer can communicate over multiple frequency bands using one or more common or shared antennas. A desire to transmit at wider bandwidth and/or over different communications networks has increased a demand for the number of bands that a wireless device can communicate over. For example, a wireless device may be specified to operate using one or more of a variety of communications standards including, for example, GSM/EDGE, IMT-2000 (3G), 4G, Long Term Evolution (LTE), Advanced LTE, IEEE 802.11 (Wi-Fi), Mobile WiMAX, Near Field Communication (NFC), Global Positioning System (GPS), GLONASS, Galileo, Bluetooth, and the like. Proprietary standards can also be applicable. The complexities of multi-band communication can be further exacerbated in configurations in which the wireless device is specified to use carrier aggregation.

The metal oxide semiconductor (MOS) capacitors, which can offer enhanced performance over certain other tunable capacitance structures. For instance, certain microelectromechanical systems (MEMS) capacitors can exhibit low Q-factor, poor reliability, and/or limited tuning range. Additionally, other approaches such as coupled resonators can suffer from large size and/or cost, and thus can be unsuitable for certain applications, including smart phones.

FIG. 5 is a schematic diagram of an integrated circuit (IC) 60 according to one embodiment. The IC 60 includes a first variable capacitor array 61, a second variable capacitor array 62, a third variable capacitor array 63, and a bias voltage generation circuit 64. The IC 60 includes a first RF input RF_(IN1), a second RF input RF_(IN2), a third RF input RF_(IN3), a first RF output RF_(OUT1), a second RF output RF_(OUT2), and a third RF output RF_(OUT3).

The first variable capacitor array 61 includes a first variable capacitor cell 71 a, a second variable capacitor cell 71 b, and a third variable capacitor cell 71 c. The first to third capacitors cells 71 a-71 c are electrically connected in parallel between the first RF input Um and the first RF output RF_(OUT1). The second variable capacitor array 62 includes a first variable capacitor cell 72 a, a second variable capacitor cell 72 b, and a third variable capacitor cell 72 c. The first to third capacitors cells 72 a 72 c are electrically connected in parallel between the second RF input RF_(IN2) and the second RF output RF_(OUT2). The third variable capacitor array 63 includes a first variable capacitor cell 73 a, a second variable capacitor cell 73 b, and a third variable capacitor cell 73 c. The first to third capacitors cells 73 a 73 c are electrically connected in parallel between the third RF input RF_(IN3) and the third RF output RF_(OUT3).

Although FIG. 5 illustrates the IC 60 as including three variable capacitor arrays, the IC 60 can be adapted to include more or fewer variable capacitor arrays. In one embodiment, the IC 60 can include between about 4 and about 16 variable capacitor arrays. In another embodiment, the IC 60 includes between about 1 and about 3 variable capacitor arrays. However, other configurations are possible.

Additionally, although FIG. 5 illustrates each variable capacitor array as including three variable capacitor cells, the variable capacitor arrays can be adapted to include more or fewer variable capacitor cells. In one embodiment, the IC 60 includes between about 6 and about 12 variable capacitor cells. However, a variable capacitor array can be adapted to include other numbers of variable capacitor cells.

The bias voltage generation circuit 64 receives the control signal CNTL, and generates a first bias voltage V_(BIAS1), a second bias voltage V_(BIAS2), and a third bias voltage V_(BIAS3). As shown in FIG. 5, the first bias voltage V_(BIAS1) is provided to the first variable capacitor cell 71 a of the first variable capacitor array 61, to the first variable capacitor cell 72 a of the second variable capacitor array 62, and to the first variable capacitor cell 73 a of the third variable capacitor array 63. Additionally, the second bias voltage V_(BIAS2) is provided to the second variable capacitor cell 71 b of the first variable capacitor array 61, to the second variable capacitor cell 72 b of the second variable capacitor array 62, and to the second variable capacitor cell 73 b of the third variable capacitor array 63. Furthermore, the third bias voltage V_(BIAS3) is provided to the third variable capacitor cell 71 c of the first variable capacitor array 61, to the third variable capacitor cell 72 c of the second variable capacitor array 62, and to the third variable capacitor cell 73 c of the third variable capacitor array 63.

The bias voltage generation circuit 64 can be used to control the voltage levels of the first, second, and third bias voltages V_(BIAS1)-V_(BIAS3) to control the capacitances of the first to third variable capacitor arrays 61-63.

The illustrated variable capacitor cells can be implemented using MOS capacitors. For example, in certain configurations, two or more pairs of anti-series MOS capacitors are cascaded to operate as a variable capacitor cell. Additionally, the first to third bias voltages V_(BIAS1)-V_(BIAS3) can be used to bias the MOS capacitors at two or more bias voltages associated with a small amount of capacitance variation, and thus with high linearity. For example, in one embodiment, the first to third bias voltages V_(BIAS1) V_(BIAS3) can be selectively controlled to bias the MOS capacitors in accumulation or inversion to control the overall capacitance of the arrays.

In certain configurations, the MOS capacitors can be fabricated using silicon on insulator (SOI) processes. However, other configurations are possible, including, for example, implementations in which the MOS capacitors are fabricated using deep sub-micron (DSM) complementary metal oxide semiconductor (CMOS) processes.

In certain configurations herein, a variable capacitor cell can include pairs of MOS capacitors implemented using anti-series configurations. Configuring a variable capacitor cell in this manner can help cancel the second-order intermodulation tones (IM2) and/or control the variation in the cell's capacitance in the presence of RF signals.

As shown in FIG. 5, the bias voltage generation circuit 64 receives the control signal CNTL, which can be used to select the voltage levels of the first, second, and third bias voltages V_(BIAS1)-V_(BIAS3). In certain configurations, each of the variable capacitor arrays 61-63 includes weighted banks of capacitors cells. For example, in one embodiment, the first variable capacitor cell 71 a, the second variable capacitor cell 71 b, and the third variable capacitor cell 71 c have different capacitance weights or sizes. For example, the variable capacitor cells of a particular variable capacitor array can increase in size by a scaling factor, such as 2.

The IC 60 includes a first signal path from the first RF input RF_(IN1) to the first RF output RF_(OUT1) through the first variable capacitor array 61. Additionally, the IC 60 includes a second signal path from the second RF input RF_(IN2) to the second RF output RF_(OUT2) through the second variable capacitor array 62, and a third signal path from the third RF input RF_(IN3) to the third RF output RF_(OUT3) through the third variable capacitor array 63.

In certain embodiments, the IC 60 does not include any switches in the signal paths between the IC's inputs and outputs through the variable capacitor arrays. By configuring the variable capacitor arrays in this manner, the variable capacitor arrays can have lower insertion loss and/or higher linearity relative to a configuration in which capacitance is provided by selecting discrete capacitors via switches.

As shown in FIG. 5, multiple variable capacitor arrays can be fabricated on a common IC, and can share control signals but receive different RF signals. However, other configurations are possible, such as implementations in which the variable capacitor arrays receive separate control signals.

FIGS. 6A and 6B are graphs of two examples of capacitance versus bias voltage. FIG. 6A includes a first graph 91 of capacitance versus voltage, and FIG. 6B includes a second graph 92 of capacitance versus voltage.

The first graph 91 includes a high frequency capacitance-voltage (CV) plot 93 for one example of an n-type MOS capacitor. As shown in the CV plot 93, the capacitance of the MOS capacitor can increase with bias voltage level. The increase in capacitance can be associated with the MOS capacitor transitioning between operating regions or modes. For example, at low bias voltage levels, the MOS capacitor can operate in an accumulation mode in which a majority carrier concentration near the gate dielectric/semiconductor interface is greater than a background majority carrier concentration of the semiconductor. Additionally, as the voltage level of the bias voltage increases, the MOS capacitor can transition from the accumulation mode to a depletion mode in which minority and majority carrier concentrations near the gate dielectric/semiconductor interface are less than the background majority carrier concentration. Furthermore, as the voltage level of the bias voltage further increases, the MOS capacitor can transition from the depletion mode to an inversion mode in which the minority carrier concentration near the gate dielectric/semiconductor interface is greater than the background majority carrier concentration.

The first graph 91 has been annotated to include an AC signal component 94 when biasing the MOS capacitor at a bias voltage level VB. When the AC signal component 94 is not present, the MOS capacitor can have a capacitance C. However, as shown by in FIG. 6A, the AC signal component 94 can generate a capacitance variation 95. The capacitance variation 95 can be associated with a capacitance variation generated by the AC signal component 94.

With reference to FIG. 6B, the second graph 92 includes the CV plot 93, which can be as described above. The second graph 92 has been annotated to include a first AC signal component 96 associated with biasing the MOS capacitor at a first bias voltage level V_(B1), and a second AC signal component 97 associated with biasing the MOS capacitor at a second bias voltage level V_(B2).

As shown in FIG. 6B, the first AC signal component 96 can generate a first capacitance variation 98, and the second AC signal component 97 can generate a second capacitance variation 99.

When biased at the first bias voltage level V_(B1) or the second bias voltage level V_(B2), the MOS capacitor can nevertheless have a capacitance that varies in the presence of AC signals. However, the first and second bias voltage levels V_(B1), V_(B2) can be associated with DC bias points of the MOS capacitor having relatively small capacitance variation or change.

Accordingly, in contrast to the capacitance variation 95 of FIG. 6A which has a relatively large magnitude, the first and second capacitance variations 98, 99 of FIG. 6B have a relatively small magnitude.

In certain embodiments herein, a variable capacitor array includes MOS capacitors that are biased at bias voltages associated with small capacitance variation. By biasing the MOS capacitors in this manner, a variable capacitor array can exhibit high linearity.

Such a variable capacitor array can also have less capacitance variation when operated in a system using multiple frequency bands. For example, when included in a tunable filter, such as a tunable notch filter and a tunable mirror filter, or a tunable matching network, the variable capacitor array can provide relatively constant capacitance even when tuned to frequency bands that are separated by a wide frequency.

In certain embodiments, the first bias voltage level V_(B1) is selected to operate in the MOS capacitor in an accumulation mode, and the second bias voltage level V_(B2) is selected to operate the MOS capacitor in an inversion mode. In certain configurations, biasing a MOS capacitor in this manner can achieve a capacitance tuning range of 3:1 or more. However, other tuning ranges can be realized, including, for example, a tuning range associated with a particular manufacturing process used to fabricate the MOS capacitor.

FIG. 7 is a schematic diagram of an IC 100 according to another embodiment. The IC 100 includes a variable capacitor array 101 and a bias voltage generation circuit 104. Although FIG. 7 illustrates a configuration in which the IC 100 includes one variable capacitor array, the IC 100 can be adapted to include additional variable capacitor arrays and/or other circuitry.

The variable capacitor array 101 includes a first variable capacitor cell 111 a, a second variable capacitor cell 111 b, and a third variable capacitor cell 111 c, which have been electrically connected in parallel between an RF input RF_(IN) and an RF output RF_(OUT). Although the illustrated variable capacitor array 101 includes three variable capacitor cells, the variable capacitor array 101 can be adapted to include more or fewer variable capacitor cells.

The bias voltage generation circuit 104 receives the control signal CNTL, and generates a first bias voltage 105 a for the first variable capacitor cell 111 a, a second bias voltage 105 b for the second variable capacitor cell 111 b, and a third bias voltage 105 c for the third variable capacitor cell 111 c.

In the illustrated configuration, the control signal CNTL can be used to set the voltage level of the first bias voltage 105 a to a first bias voltage level V_(B1) or to a second bias voltage level V_(B2). Similarly, the control signal CNTL can be used to set the voltage level of the second bias voltage 105 b to the first bias voltage level V_(B1) or to the second bias voltage level V_(B2), and to set the voltage level of the third bias voltage 105 c to the first bias voltage level V_(B1) or to the second bias voltage level V_(B2).

By controlling the voltage levels of the bias voltages to the first or second bias voltage levels V_(B1), V_(B2), the variable capacitor array 101 can exhibit a small variation in capacitance in the presence of an RF signal at the RF input RF_(IN). Accordingly, the variable capacitor array 101 can exhibit high linearity in the presence of RF signals.

The control signal CNTL can control an overall capacitance of the variable capacitor array 101. For example, the size of the first, second, and third MOS capacitors cells 111 a 111 c can be weighted relative to one another, and an overall capacitance of the variable capacitor array 101 can be based on a sum of the capacitances of the array's variable capacitor cells.

In one embodiment, the variable capacitor array's variable capacitor cells are scaled by a factor of 2, and each of the variable capacitor cells includes k pairs of anti-series MOS capacitors connected in a cascade. For example, a second variable capacitor cell of the variable capacitor array can have a size that is about a factor of 2 relative to a first variable capacitor cell of the variable capacitor array. Additionally, an nth variable capacitor cell in the array can have a size that is about 2^(n-1) that of the first variable capacitor cell, where n is an integer greater than or equal to 2. Although one possible variable capacitor array sizing scheme has been described, other configurations are possible.

When a variable capacitor array includes n variable capacitor cells that are scaled by a factor of 2 relative to one another and that include k pairs of anti-series MOS capacitors in a cascade, the bias voltage generation circuit 104 can control the array's first variable capacitor cell to a capacitance of C₁/2k or C₂/2k by biasing the first variable capacitor cell with the first bias voltage level V_(B1) or the second bias voltage level V_(B2). Additionally, the bias voltage generation circuit 104 can control the array's second variable capacitor cell to a capacitance of 2¹*C₁/2k or 2¹*C₂/2k by biasing the second variable capacitor cell with the first bias voltage level V_(B1) or the second bias voltage level VB2. Furthermore, the bias voltage generation circuit 104 can control the array's nth variable capacitor cell to a capacitance of 2^(n-1)*C₁/2k or 2^(n-1)*C₂/2k by biasing the nth variable capacitor cell with the first bias voltage level V_(B1) or the second bias voltage level V_(B2).

Configuring the bias voltage generation circuit 104 to control a bias voltage to one of two voltage levels can simplify a coding scheme associated with the control signal CNTL. For example, in such a configuration, the control signal CNTL can comprise a digital control signal, and individual bits of the digital control signal can be used to control the array's bias voltages to a particular bias voltage level. Although one possible coding scheme of the control signal CNTL has been described, other configurations are possible.

FIG. 8 is a schematic diagram of an IC 120 according to another embodiment. The IC 120 includes a variable capacitor array 121 and a bias voltage generation circuit 124. Although FIG. 8 illustrates a configuration in which the IC 120 includes one variable capacitor array, the IC 100 can be adapted to include additional variable capacitor arrays and/or other circuitry.

The variable capacitor array 121 includes a first variable capacitor cell 121 a, a second variable capacitor cell 121 b, and a third variable capacitor cell 121 c, which have been electrically connected in parallel between an RF input RF_(IN) and an RF output RF_(OUT). The first variable capacitor cell 121 a includes a cascade of a first pair of anti-series MOS capacitors 141 a, a second pair of anti-series MOS capacitors 141 b, and a third pair of anti-series MOS capacitors 141 c. The second variable capacitor cell 121 b includes a cascade of a first pair of anti-series MOS capacitors 142 a, a second pair of anti-series MOS capacitors 142 b, and a third pair of anti-series MOS capacitors 142 c. The third variable capacitor cell 121 c includes a cascade of a first pair of anti-series MOS capacitors 143 a, a second pair of anti-series MOS capacitors 143 b, and a third pair of anti-series MOS capacitors 143 c. Although the illustrated variable capacitor array 121 includes three variable capacitor cells, the variable capacitor array 121 can be adapted to include more or fewer variable capacitor cells. Additionally, although the illustrated variable capacitor cells each include a cascade of three pairs of anti-series MOS capacitors, the variable capacitor cells can include more or fewer pairs of anti-series MOS capacitors.

The bias voltage generation circuit 124 receives the control signal CNTL, and generates a first bias voltage V_(BIAS1) for the first variable capacitor cell 131 a, a second bias voltage V_(BIAS2) for the second variable capacitor cell 131 b, and a third bias voltage V_(BIAS3) for the third variable capacitor cell 131 c. In certain configurations, the bias voltage generation circuit 124 can also be used to generate a body bias voltage V_(BODY), which can be used to control the body voltages of MOS capacitors of the variable capacitor array 121.

Additional details of the integrated circuit 120 can be similar to those described earlier.

FIG. 9A is a schematic diagram of a variable capacitor cell 150 according to one embodiment. The variable capacitor cell 150 includes a first pair of anti-series MOS capacitors 151, a second pair of anti-series MOS capacitors 152, a third pair of anti-series MOS capacitors 153, a first DC biasing resistor 171, a second DC biasing resistor 172, a third DC biasing resistor 173, a fourth DC biasing resistor 174, a first control biasing resistor 181, a second control biasing resistor 182, and a third control biasing resistor 183.

Although the variable capacitor cell 150 is illustrated as including three pairs of anti-series MOS capacitors, the teachings herein are applicable to configurations including more or fewer pairs of anti-series MOS capacitors. For example, in one embodiment, a variable capacitor cell includes a cascade of between 2 and 18 pairs of anti-series MOS capacitors.

In the illustrated configuration, each of the pairs of anti-series MOS capacitors 151-153 includes two MOS capacitors electrically connected in anti-series or inverse series. For example, the first pair of anti-series MOS capacitors 151 includes a first MOS capacitor 161 and a second MOS capacitor 162. The first and second MOS capacitors 161, 162 have anodes associated with transistor gates and cathodes associated with transistor source and drain regions. As shown in FIG. 9A, the anode of the first MOS capacitor 161 is electrically connected to the anode of the second MOS capacitor 162. Additionally, the second pair of anti-series MOS capacitors 152 includes a third MOS capacitor 163 and a fourth MOS capacitor 164, and the anode of the third MOS capacitor 163 is electrically connected to the anode of the fourth MOS capacitor 164. Furthermore, the third pair of anti-series MOS capacitors 153 includes fifth MOS capacitor 165 and a sixth MOS capacitor 166, and the anode of the fifth MOS capacitor 165 is electrically connected to the anode of the sixth MOS capacitor 166.

As shown in FIG. 9A, the first to third pairs of anti-series MOS capacitors 151-153 are arranged in a cascade between the RF input RF_(IN) and the RF output RF_(OUT). For example, the cathode of the first MOS capacitor 161 is electrically connected to the RF input RF_(IN), and the cathode of the second MOS capacitor 162 is electrically connected to the cathode of the third MOS capacitor 163. Additionally, the cathode of the fourth MOS capacitor 164 is electrically connected to the cathode of the fifth MOS capacitor 165, and a cathode of the sixth MOS capacitor 166 is electrically connected to the RF output RF_(OUT).

Arranging two or more pairs of anti-series MOS capacitors in a cascade can increase a voltage handling capability of a variable capacitor cell relative to a configuration including a single pair of anti-series MOS capacitors. For example, arranging two or more pairs of anti-series MOS capacitors in a cascade can increase a voltage handling and/or power handling capability of the variable capacitor cell by distributing RF signal voltage across multiple MOS capacitors.

Accordingly, cascading several pairs of anti-series MOS capacitors can achieve high voltage operation of a variable capacitor cell.

Additionally, the illustrated variable capacitor cell 150 includes pairs of MOS capacitors that are electrically connected in anti-series, which can decrease capacitance variation in the presence of RF signals. For example, when the first and second variable capacitors are each biased with a particular bias voltage, the variable capacitors' capacitance may change when an RF input signal is received on the RF input RF_(IN). However, a capacitance variation ΔC between MOS capacitors in a given pair can have about equal magnitude, but opposite polarity.

For instance, in the presence of an RF input signal that generates a capacitance variation having a magnitude ΔC, a first MOS capacitor of a pair of anti-series MOS capacitors may have a capacitance C_(V)+ΔC, while the second MOS capacitor may have a capacitance C_(V)−ΔC. Thus, the total capacitance of the anti-series combination of the first and second MOS capacitors 121, 122 can be about equal to ½C_(V)½ΔC²/C_(V). Since ½ΔC² is typically much smaller than ΔC, the anti-series MOS capacitors can exhibit small capacitance variation when RF signals propagate through the variable capacitor cell.

Accordingly, the illustrated variable capacitor cell 150 can provide reduced capacitance variation in the presence of RF signals.

In the illustrated configuration, the first to fourth DC biasing resistors 171-174 have been used to bias the cathodes of the MOS capacitors 161-166 with the first voltage V₁, which can be a ground, power low supply, or other reference voltage in certain implementations. Additionally, the first to third control biasing resistors 181-183 are used to bias the anodes of the MOS capacitors 161-166 with the bias voltage V_(BIAS).

In one embodiment, the DC biasing resistors 171-174 have a resistance selected in the range of 10 kΩ to 10,000 kΩ, and the control biasing resistors 181-183 have a resistance selected in the range of 10 kΩ to 10,000 kΩ. Although one example of resistance values have been provided, other configurations are possible. For example, choosing relatively low resistance values for the biasing resistors can increase control over DC biasing conditions, but can also undesirably increase signal loss and/or degrade linearity since the resistors operate in shunt to an RF signal propagating through the variable capacitor cell. Accordingly, resistance values can vary depending on application, fabrication process, and/or desired performance specifications.

The bias voltages across the MOS capacitors 161-166 can be based on a voltage difference between the bias voltage V_(BIAS) and the first voltage V₁. Additionally, a bias voltage generation circuit, such as the bias voltage generation circuit 64 of FIG. 5, can be used to control a voltage level of the bias voltage V_(BIAS) to control the variable capacitor cell's capacitance between the RF input RF_(IN) and the RF output RF_(OUT).

In certain configurations, the bias voltage generation circuit can control the bias voltage V_(BIAS) to a voltage level selected from a discrete number of two or more bias voltage levels associated with high linearity. Thus, rather than biasing the MOS capacitors at a bias voltage level selected from a continuous tuning voltage range, the bias voltage generation circuit generates the MOS capacitors' bias voltages by selecting a particular cell's bias voltage level from a discrete set of bias voltage levels associated with high linearity. In one embodiment, the bias voltage generation circuit biases a particular MOS capacitor either at a first bias voltage level associated with an accumulation mode of the MOS capacitor or at a second bias voltage level associated an inversion mode of the MOS capacitor.

Biasing the MOS capacitors 161-166 in this manner can improve linearity relative to a configuration in which the MOS capacitors 161-166 are biased at a bias voltage level selected from a continuous tuning voltage range. For example, a MOS capacitor can exhibit a change in capacitance in response to changes in an applied RF signal, and a magnitude of the capacitance change can vary with the MOS capacitor's bias voltage level.

Accordingly, the illustrated variable capacitor cell 150 can provide high linearity between the RF input RF_(IN) and the RF output RF_(OUT).

FIG. 9B is a circuit diagram of a variable capacitor cell 160 according to one embodiment. The variable capacitor cell 160 includes a first pair of anti-series MOS capacitors 191, a second pair of anti-series MOS capacitors 192, a third pair of anti-series MOS capacitors 193, a first DC biasing resistor 171, a second DC biasing resistor 172, a third DC biasing resistor 173, a fourth DC biasing resistor 174, a first control biasing resistor 181, a second control biasing resistor 182, and a third control biasing resistor 183. Although the variable capacitor cell 160 is illustrated as including three pairs of anti-series MOS capacitors, the teachings herein are applicable to configurations including more or fewer pairs of anti-series MOS capacitors.

The variable capacitor cell 160 of FIG. 9B is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 160 illustrates a different anti-series configuration of the pairs of anti-series MOS capacitors 191-193.

In particular, in contrast to the variable capacitor cell 150 of FIG. 9A in which the anodes of the MOS capacitors of a given pair are electrically connected to one another, the variable capacitor cell 160 of FIG. 9B illustrates a configuration in which the cathodes of a given pair of MOS capacitors are electrically connected to one another. For example, the first pair of MOS capacitors 191 includes a first MOS capacitor 201 and a second MOS capacitor 202, and the cathodes of the first and second MOS capacitors 201, 202 are electrically connected to one another. Similarly, the second pair of MOS capacitors 192 includes a third MOS capacitor 203 and a fourth MOS capacitor 204, and the cathodes of the third and fourth MOS capacitors 203, 204 are electrically connected to one another. Likewise, the third pair of MOS capacitors 193 includes a fifth MOS capacitor 205 and a sixth MOS capacitor 206, and the cathodes of the fifth and sixth MOS capacitors 205, 206 are electrically connected to one another.

As shown in FIG. 9B, the pairs of anti-series MOS capacitors 191-193 are electrically connected in a cascade between the RF input RF_(IN) and the RF output RF_(OUT). For example, the anode of the first MOS capacitor 201 is electrically connected to the RF input RF_(IN), and the anode of the second MOS capacitor 202 is electrically connected to the anode of the third MOS capacitor 203. Additionally, the anode of the fourth MOS capacitor 204 is electrically connected to the anode of the fifth MOS capacitor 205, and an anode of the sixth MOS capacitor 206 is electrically connected to the RF output RF_(OUT).

In the illustrated configuration, the first to fourth DC biasing resistors 171 174 are used to bias the anodes of the MOS capacitors 201-206 with the first voltage V₁, which can be a ground, power low supply, or other reference voltage in certain implementations. Additionally, the first to third control biasing resistors 181-183 are used to bias the cathodes of the MOS capacitors 201-206 with the bias voltage V_(BIAS).

In certain configurations, the variable capacitor cell 150 of FIG. 9A can be more robust against damage from electrostatic discharge (ESD) events relative to the variable capacitor cell 160 of FIG. 9B.

For example, the RF input RF_(IN) and RF output RF_(OUT) of a variable capacitor cell may be electrically connected to input and output pins of an IC on which the variable capacitor cell is fabricated. Since a MOS capacitor's source and drain regions typically can withstand a greater voltage relative to the MOS capacitor's gate region when fabricated using certain manufacturing processes, the variable capacitor cell 150 of FIG. 9A may exhibit a greater robustness to ESD events or other overvoltage conditions relative to the variable capacitor cell 160 of FIG. 9B.

Additional details of the variable capacitor cell 160 can be similar to those described earlier.

FIG. 10A is a variable capacitor cell 220 according to another embodiment. The variable capacitor cell 220 of FIG. 10A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 220 of FIG. 10A further includes a first diode 221, a second diode 222, a third diode 223, a fourth diode 224, a fifth diode 225, and a sixth diode 226.

As shown in FIG. 10A, the diodes 221-226 are electrically connected between the body and gate of the MOS capacitors 161-166, respectively. In particular, the anodes of the diodes 221-226 are electrically connected to the bodies of the MOS capacitors 161-166, respectively, and the cathodes of the diodes 221-226 are electrically connected to the gates of the MOS capacitors 161-166, respectively. The diodes 221-226 can be included in a variety of manufacturing processes, such as silicon-on-insulator (SOI) processes. In certain configurations, the diodes 221-226 are implemented as p-n junction diodes. For example, an n-type MOS capacitor can include a p-type body region, and an n-type active region can be included in the p-type body region and electrically connected to the gate via metallization to provide a forward p-n junction diode from body to gate.

Including the diodes 221-226 can enhance the performance in the presence of RF signaling conditions, including, for example, enhanced performance in the presence of voltage changes to an RF signal over a signal cycle. For example, the diodes 221-226 can increase voltage headroom of the MOS capacitors 161-166 relative to a configuration in which the diodes 221-226 are omitted. Additionally, the diodes 221-226 can aid in better distributing an RF signal voltage across the MOS capacitors 161-166, thereby preventing large voltage build-up across a particular MOS capacitor in the cascade. Thus, the illustrated configuration can exhibit greater signal handling and/or power handling capability relative to a configuration that omits the diodes 221-226.

Additional details of the variable capacitor cell 220 can be similar to those described earlier.

FIG. 10B is a circuit diagram of a variable capacitor cell 230 according to another embodiment. The variable capacitor cell 230 of FIG. 10B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 230 of FIG. 10B further includes the first to sixth diodes 221-226.

As shown in FIG. 10B, the anodes of the diodes 221-226 are electrically connected to the bodies of the MOS capacitors 201-206, respectively, and the cathodes of the diodes 221-226 are electrically connected to the gates of the MOS capacitors 201-206, respectively. Including the diodes 221-226 can improve RF signal voltage distribution and/or increase voltage headroom of the MOS capacitors 201-206.

Additional details of the variable capacitor cell 230 can be similar to those described earlier.

FIG. 11A is a circuit diagram of a variable capacitor cell 240 according to another embodiment. The variable capacitor cell 240 of FIG. 11A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 240 of FIG. 11A further includes a first body biasing resistor 241, a second body biasing resistor 242, a third body biasing resistor 243, a fourth body biasing resistor 244, a fifth body biasing resistor 245, and a sixth body biasing resistor 246.

The body biasing resistor 241-246 are used to bias the bodies of the MOS capacitors 161-166 with a body bias voltage V_(BODY). Including the body biasing resistors 241-246 can aid in increasing the voltage headroom of the MOS capacitors 161-166 in the presence of RF voltage swing. In certain configurations, the body bias voltage V_(BODY) is generated by a bias voltage generation circuit, such as the bias voltage generation circuit 124 of FIG. 8.

The body biasing resistors 241-246 can have any suitable resistance value. In one embodiment, the body biasing resistors 241-246 have a resistance selected in the range of 10 kΩ to 10,000 kΩ. Although one example of resistance values have been provided, other configurations are possible, such as resistance values selected for a particular application, fabrication process, and/or desired performance specifications.

Additional details of the variable capacitor cell 240 can be similar to those described earlier.

FIG. 11B is a circuit diagram of a variable capacitor cell 250 according to another embodiment. The variable capacitor cell 250 of FIG. 11B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 250 of FIG. 11B further includes the first to sixth body biasing resistors 241 246.

As shown in FIG. 11B, the body biasing resistors 241 246 are electrically connected between the body bias voltage V_(BODY) and the bodies of the MOS capacitors 201-206, respectively. Including the body biasing resistors 241 246 can increase voltage headroom of the MOS capacitors 201 206 in the presence of amplitude change or swing of an RF signal.

Additional details of the variable capacitor cell 250 can be similar to those described earlier.

FIG. 12A is a circuit diagram of a variable capacitor cell 260 according to another embodiment. The variable capacitor cell 260 of FIG. 12A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 260 of FIG. 12A further includes a first signal swing compensation capacitor 261, a second signal swing compensation capacitor 262, and a third signal swing compensation capacitor 263.

As shown in FIG. 12A, the first signal swing compensation capacitor 261 is electrically connected in parallel with the first pair of anti-series MOS capacitors 151. For example, the first signal swing compensation capacitor 261 includes a first end electrically connected to the cathode of the first MOS capacitor 161 and a second end electrically connected to the cathode of the second MOS capacitor 162. Similarly, the second signal swing compensation capacitor 262 is electrically connected in parallel with the second pair of anti-series MOS capacitors 152, and the third signal swing compensation capacitor 263 is electrically connected in parallel with the third pair of anti-series MOS capacitors 153.

The signal swing compensation capacitors 261-263 can be used to balance or compensate for differences in voltage, current, and/or phase between pairs of anti-series MOS capacitors. Absent compensation, variation in voltage, current, and/or phase between MOS capacitors may degrade the variable capacitor cell's linearity.

In certain configurations, the capacitance values of the signal swing compensation capacitors 261-263 can be individually selected to improve voltage, current, and/or phase balancing between MOS capacitors 161-166. For example, even when the MOS capacitors 161-166 are implemented with the same size and/or geometry, the capacitance values of the signal switch compensation capacitors 261-263 can be individually selected to provide improve compensation in the presence of RF signaling conditions. In one embodiment, the first signal swing compensation capacitor 261 has a capacitance value that is greater than that of the second signal swing compensation capacitor 262, and the second signal swing compensation capacitor 262 has a capacitance value that is greater than that of the third signal swing compensation capacitor 263. Sizing the signal swing compensation capacitors in this manner may provide enhanced balancing in certain configurations, such as configurations in which large amplitude RF signals are received at the RF input RF_(IN).

Additional details of the variable capacitor cell 260 can be similar to those described earlier.

FIG. 12B is a circuit diagram of a variable capacitor cell 270 according to another embodiment. The variable capacitor cell 270 of FIG. 12B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 270 of FIG. 12B further includes the signal swing compensation capacitors 261-263.

As shown in FIG. 12B, the first signal swing compensation capacitor 261 is electrically connected in parallel with the first pair of anti-series MOS capacitors 191. For example, the first signal swing compensation capacitor 261 includes a first end electrically connected to the anode of the first MOS capacitor 201 and a second end electrically connected to the anode of the second MOS capacitor 202. Similarly, the second signal swing compensation capacitor 262 is electrically connected in parallel with the second pair of anti-series MOS capacitors 192, and the third signal swing compensation capacitor 263 is electrically connected in parallel with the third pair of anti-series MOS capacitors 193.

The signal swing compensation capacitors 261-263 can be included to balance differences in voltage, current, and/or phase between adjacent MOS capacitors, thereby improving linearity of the variable capacitor cell.

Additional details of the variable capacitor cell 270 can be similar to those described earlier.

FIG. 13A is a circuit diagram of a variable capacitor cell 280 according to another embodiment. The variable capacitor cell 280 of FIG. 13A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 280 of FIG. 13A further includes the diodes 221-226 and the signal swing compensation capacitors 261-263.

Additional details of the variable capacitor cell 280 can be similar to those described earlier.

FIG. 13B is a circuit diagram of a variable capacitor cell 290 according to another embodiment. The variable capacitor cell 290 of FIG. 13B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 290 of FIG. 13B further includes the diodes 221-226 and the signal swing compensation capacitors 261-263.

Additional details of the variable capacitor cell 290 can be similar to those described earlier.

FIG. 14A is a circuit diagram of a variable capacitor cell 300 according to another embodiment. The variable capacitor cell 300 of FIG. 14A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 300 of FIG. 14A further includes the body biasing resistors 241-246 and the signal swing compensation capacitors 261-263.

Additional details of the variable capacitor cell 300 can be similar to those described earlier.

FIG. 14B is a circuit diagram of a variable capacitor cell 310 according to another embodiment. The variable capacitor cell 310 of FIG. 14B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 310 of FIG. 14B further includes the body biasing resistors 241-246 and the signal swing compensation capacitors 261-263.

Additional details of the variable capacitor cell 310 can be similar to those described earlier.

FIG. 15A is a circuit diagram of a variable capacitor cell 320 according to another embodiment. The variable capacitor cell 320 of FIG. 15A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 320 of FIG. 15A further includes a first drift protection resistor 321, a second drift protection resistor 322, and a third drift protection resistor 323.

As shown in FIG. 15A, the first drift protection resistor 321 is electrically connected in parallel with the first pair of anti-series MOS capacitors 151. For example, the first drift protection resistor 321 includes a first end electrically connected to the cathode of the first MOS capacitor 161 and a second end electrically connected to the cathode of the second MOS capacitor 162. Similarly, the second drift protection resistor 322 is electrically connected in parallel with the second pair of anti-series MOS capacitors 152, and the third drift protection resistor 323 is electrically connected in parallel with the third pair of anti-series MOS capacitors 153.

The drift protection resistor 321-323 can be used to balance DC operating points across the MOS capacitors 161-166, thereby enhancing performance in the presence of RF amplitude variation or swing. As described earlier, a capacitance provided by a MOS capacitor changes with a voltage difference across the MOS capacitor's anode and cathode. Accordingly, balancing the DC operating point across the MOS capacitors 161-166 can help prevent the capacitances values of the MOS capacitors 161-166 from drifting and becoming unstable in the presence of RF signaling conditions.

In one embodiment, the drift protection resistors 321-323 have a resistance selected in the range of 5 kΩ to 1,000 kΩ. Although one example of resistance values have been provided, other configurations are possible. For example, choosing relatively low resistance values for the drift protection resistors can reduce capacitance value drift due to RF signal swing, but can also impact signaling performance since the resistors are electrically in series between the RF input RF_(IN) and the RF output RF_(OUT). Accordingly, resistance values can vary depending on application, fabrication process, and/or desired performance specifications.

Additional details of the variable capacitor cell 320 can be similar to those described earlier.

FIG. 15B is a circuit diagram of a variable capacitor cell 330 according to another embodiment. The variable capacitor cell 330 of FIG. 15B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 330 of FIG. 15B further includes the drift protection resistors 321-323.

As shown in FIG. 15B, the first drift protection resistor 321 is electrically connected in parallel with the first pair of anti-series MOS capacitors 191. For example, the first drift protection resistor 321 includes a first end electrically connected to the anode of the first MOS capacitor 201 and a second end electrically connected to the anode of the second MOS capacitor 202. Similarly, the second drift protection resistor 322 is electrically connected in parallel with the second pair of anti-series MOS capacitors 192, and the third drift protection resistor 323 is electrically connected in parallel with the third pair of anti-series MOS capacitors 193.

The drift protection resistors 321-323 can be included to prevent the capacitances values of the MOS capacitors 201-206 from drifting and becoming unstable in the presence of RF signaling conditions.

Additional details of the variable capacitor cell 330 can be similar to those described earlier.

FIG. 16A is a circuit diagram of a variable capacitor cell 340 according to another embodiment. The variable capacitor cell 340 of FIG. 16A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 340 of FIG. 16A further includes the diodes 221-226 and the drift protection resistors 321-323.

Additional details of the variable capacitor cell 340 can be similar to those described earlier.

FIG. 16B is a circuit diagram of a variable capacitor cell 350 according to another embodiment. The variable capacitor cell 350 of FIG. 16B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 350 of FIG. 16B further includes the diodes 221-226 and the drift protection resistors 321-323.

Additional details of the variable capacitor cell 350 can be similar to those described earlier.

FIG. 17A is a circuit diagram of a variable capacitor cell 360 according to another embodiment. The variable capacitor cell 360 of FIG. 17A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 360 of FIG. 17A further includes the body biasing resistors 241-246 and the drift protection resistors 321-323.

Additional details of the variable capacitor cell 360 can be similar to those described earlier.

FIG. 17B is a circuit diagram of a variable capacitor cell 370 according to another embodiment. The variable capacitor cell 370 of FIG. 17B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 370 of FIG. 17B further includes the body biasing resistors 241-246 and the drift protection resistors 321-323.

Additional details of the variable capacitor cell 370 can be similar to those described earlier.

FIG. 18A is a circuit diagram of a variable capacitor cell 380 according to another embodiment. The variable capacitor cell 380 of FIG. 18A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 380 of FIG. 18A further includes a first feed forward capacitor 381, a second feed-forward capacitor 382, and a third feed forward capacitor 383.

As shown in FIG. 18A, the first feed forward capacitor 381 is electrically connected between the RF input RF_(IN) and an intermediate node of the first pair of anti-series MOS capacitors 151. For example, the first feed forward capacitor 381 is electrically connected between the RF input RF_(IN) and the anodes of the first and second MOS capacitors 161, 162. Additionally, the second feed-forward capacitor 382 is electrically connected between the intermediate node of the first pair of anti-series MOS capacitors 151 and an intermediate node of the second pair of anti-series MOS capacitors 152. For example, the second feed forward capacitor 382 includes a first end electrically connected to the anodes of the first and second MOS capacitors 161, 162 and a second end electrically connected to anodes of the third and fourth MOS capacitors 163, 164. Furthermore, the third feed forward capacitor 383 is electrically connected between the intermediate node of the second pair of anti-series MOS capacitors 152 and an intermediate node of the third pair of anti-series MOS capacitors 153. For example, the third feed forward capacitor 383 includes a first end electrically connected to the anodes of the third and fourth MOS capacitors 163, 164, and a second end electrically connected to anodes of the fifth and sixth MOS capacitors 165, 166.

The feed forward capacitors 381-383 can be used to balance or compensate for differences in voltage, current, and/or phase between MOS capacitors. For example, the feed forward capacitors 381-383 can be used to balance an RF voltage drop across the MOS capacitors 161-166, thereby improving the linearity of the variable capacitor cell.

In certain configurations, the feed forward capacitors 381-383 can be individually selected to improve voltage, current, and/or phase balancing between MOS capacitors 161-166. For example, even when the MOS capacitors 161-166 are implemented with the same size and/or geometry, the capacitance values of the feed forward capacitors 381-383 can be individually selected to provide improve compensation in the presence of RF signaling conditions. In one embodiment, the first feed forward capacitor 381 has a capacitance value that is greater than that of the second feed forward capacitor 382, and the second feed forward capacitor 382 has a capacitance value that is greater than that of the third feed forward capacitor 383. Sizing the feed forward capacitors in this manner may provide enhanced balancing in certain configurations, such as configurations in which large amplitude RF signals are received at the RF input RF_(IN).

Additional details of the variable capacitor cell 380 can be similar to those described earlier.

FIG. 18B is a circuit diagram of a variable capacitor cell 390 according to another embodiment. The variable capacitor cell 390 of FIG. 18B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 390 of FIG. 18B further includes the feed forward capacitors 381-383.

As shown in FIG. 18B, the first feed forward capacitor 381 is electrically connected between the RF input RF_(IN) and an intermediate node of the first pair of anti-series MOS capacitors 191. For example, the first feed forward capacitor 381 is electrically connected between the RF input RF_(IN) and the cathodes of the first and second MOS capacitors 201, 202. Additionally, the second feed-forward capacitor 382 is electrically connected between the intermediate node of the first pair of anti-series MOS capacitors 191 and an intermediate node of the second pair of anti-series MOS capacitors 192. For example, the second feed forward capacitor 382 includes a first end electrically connected to the cathodes of the first and second MOS capacitors 201, 202 and a second end electrically connected to cathodes of the third and fourth MOS capacitors 203, 204. Furthermore, the third feed forward capacitor 383 is electrically connected between the intermediate node of the second pair of anti-series MOS capacitors 192 and an intermediate node of the third pair of anti-series MOS capacitors 193. For example, the third feed forward capacitor 383 includes a first end electrically connected to the cathodes of the third and fourth MOS capacitors 203, 204, and a second end electrically connected to cathodes of the fifth and sixth MOS capacitors 205, 206.

The feed forward capacitors 381 383 can be included to balance differences in voltage, current, and/or phase between MOS capacitors, thereby improving linearity of the variable capacitor cell.

Additional details of the variable capacitor cell 390 can be similar to those described earlier.

FIG. 19A is a circuit diagram of a variable capacitor cell 400 according to another embodiment. The variable capacitor cell 400 of FIG. 19A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 400 of FIG. 19A further includes the diodes 221-226 and the feed forward capacitors 381-383.

Additional details of the variable capacitor cell 400 can be similar to those described earlier.

FIG. 19B is a circuit diagram of a variable capacitor cell 410 according to another embodiment. The variable capacitor cell 410 of FIG. 19B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 410 of FIG. 19B further includes the diodes 221-226 and the feed forward capacitors 381-383.

Additional details of the variable capacitor cell 410 can be similar to those described earlier.

FIG. 20A is a circuit diagram of a variable capacitor cell 420 according to another embodiment. The variable capacitor cell 420 of FIG. 20A is similar to the variable capacitor cell 150 of FIG. 9A, except that the variable capacitor cell 420 of FIG. 20A further includes the body biasing resistors 241-246 and the feed forward capacitors 381-383.

Additional details of the variable capacitor cell 420 can be similar to those described earlier.

FIG. 20B is a circuit diagram of a variable capacitor cell 430 according to another embodiment. The variable capacitor cell 430 of FIG. 20B is similar to the variable capacitor cell 160 of FIG. 9B, except that the variable capacitor cell 430 of FIG. 20B further includes the body biasing resistors 241-246 and the feed forward capacitors 381-383.

Additional details of the variable capacitor cell 430 can be similar to those described earlier.

FIG. 21A is a circuit diagram of a variable capacitor cell 440 according to another embodiment. The variable capacitor cell 440 of FIG. 21A is similar to the variable capacitor cell 320 of FIG. 15A, except that the variable capacitor cell 440 of FIG. 21A omits the first to fourth DC biasing resistors 171-174.

As described earlier, the drift protection resistor 321-323 can be used to balance DC operating points across the MOS capacitors 161-166, thereby enhancing performance in the presence of RF amplitude variation or swing. In the illustrated configuration, the first to fourth DC biasing resistors 171-174 have been omitted in favor of controlling the DC bias voltage at the cathodes of the MOS capacitors 161-166 using the drift protection resistors 321-323. For example, in the illustrated configuration, the DC bias voltage at the cathodes of the MOS capacitors 161-166 can be controlled to a DC bias voltage of the RF input RF_(IN) and RF output RF_(OUT). Additionally, one of the terminals RF_(IN) or RF_(OUT) may be grounded when used in a shunt configuration, thus eliminating the need of first to fourth DC biasing resistors 171-174.

Additional details of the variable capacitor cell 440 can be similar to those described earlier.

FIG. 21B is a circuit diagram of a variable capacitor cell 450 according to another embodiment. The variable capacitor cell 450 of FIG. 21B is similar to the variable capacitor cell 330 of FIG. 15B, except that the variable capacitor cell 450 of FIG. 21B omits the first to fourth DC biasing resistors 171-174.

As shown in FIG. 21B, the first to fourth DC biasing resistors 171-174 have been omitted in favor of controlling the DC bias voltage at the anodes of the MOS capacitors 201-206 using the drift protection resistors 321-323. In the illustrated configuration, the DC bias voltage at the anodes of the MOS capacitors 201-206 can be controlled to the DC bias voltage of the RF input RF_(IN) and the RF output RF_(OUT).

Additional details of the variable capacitor cell 450 can be similar to those described earlier.

Although FIGS. 9A-21B illustrate implementations MOS capacitors using n-type MOS (NMOS) capacitors, the teachings herein are also applicable to configurations using p type MOS (PMOS) capacitors.

Additionally, although various embodiments of variable capacitor cells are shown in FIGS. 9A-21B, the teachings herein are also applicable to variable capacitor cells including a different combination of features. For example, to achieve a desired performance for a particular application and/or manufacturing process, a variable capacitor cell can include any suitable combination of features of the embodiments of FIGS. 9A-21B.

FIG. 22 is a schematic diagram of a cross section of an IC 3002 according to one embodiment. The IC 3002 includes a support substrate 3010, a buried oxide (BOX) layer 3020 over the support substrate 3010, and a device layer 3030 over the BOX layer 3020. The IC 3002 further includes a substrate contact 3040, which has been provided through the BOX layer 3020 and the device layer 3030 to provide electrical contact to the support substrate 3010.

The illustrated IC 3002 further includes a first MOS capacitor 3110 a and a second MOS capacitor 3110 b. The first MOS capacitor 3110 a includes source and drain regions 3210 a, 3210 b, respectively, which collectively operate as the first MOS capacitor's cathode. The first MOS capacitor 3110 a further includes a first gate region 3230 a, which is disposed over a first gate oxide region 3220 a and which operates as the first MOS capacitor's anode. The second MOS capacitor 3110 b includes source and drain regions 3210 c, 3210 d, respectively, which collectively operate as the second MOS capacitor's cathode. The second MOS capacitor 3110 b further includes a second gate region 3230 b, which is disposed over a second gate oxide region 3220 b and which operates as the second MOS capacitor's anode.

In the illustrated configuration, isolation regions have been used to help isolate the first and second MOS capacitors 3110 a, 3110 b from one another and from other structures of the IC 3002. For example, the first MOS capacitor 3110 a is positioned between the first and second isolation regions 3250 a, 3250 b, and the second MOS capacitor 3110 b is positioned between the second and third isolation regions 3250 b, 3250 c. In certain configurations, isolation regions can be used to surround a perimeter of the first and second MOS capacitors 3110 a, 3110 b when viewed from above. In one embodiment, the first and second MOS capacitors 3110 a, 3110 b are associated with two different variable capacitor arrays.

Despite inclusion of the isolation regions 3250 a 3250 c, parasitic circuit components can result in parasitic coupling between the first and second MOS capacitors 3110 a, 3110 b. For example, a first parasitic capacitor CPAR1 can be present between the cathode of the first MOS capacitor 3110 a and the BOX layer 3020 and/or the support substrate 3010, and a second parasitic capacitor CPAR2 can be present between the cathode of the second MOS capacitor 3110 b and the BOX layer 3020 and/or the support substrate 3010. Additionally, the first and second parasitic capacitors CPAR1, CPAR2 can be electrically connected to one another via a parasitic resistor RPAR, which can be associated with a resistance of the BOX layer 3020 and/or the support substrate 3010.

Although a capacitance of the first and second parasitic capacitors CPAR1, CPAR2 can be relatively small and a resistance of the parasitic resistor RPAR can be relatively large, parasitic coupling can nevertheless be present between the first and second MOS capacitors 3110 a, 3110 b. The parasitic coupling can lead to a degradation of the Q-factor of variable capacitor array that includes the first and second MOS capacitors 3110 a, 3110 b.

The IC 3002 has been annotated to include the substrate bias circuit 3120, which can be used to control a voltage level of the support substrate 3010. For clarity of the figures, the substrate bias circuit 3120 has been illustrated schematically as a box. However, the substrate bias circuit 3120 can be fabricated on the IC 3002.

In certain configurations, the substrate bias circuit 3120 can be used to control the voltage level of the support substrate 3010 so as to increase a resistivity of the parasitic resistor RPAR relative to a configuration in which the support substrate 3010 is unbiased or electrically floating. For example, positive fixed charge in the BOX layer 3020 can attract electrons to an interface between the BOX layer 3020 and the support substrate 3010, which can lead to an inversion or accumulation layer at the interface. The inversion layer can have a resistance that is much smaller than a resistance of the BOX layer 3020, and thus can serve to increase parasitic coupling between the first and second MOS capacitors 3110 a, 3110 b, which can degrade Q-factor.

By biasing the support substrate 3010 using the substrate bias circuit 3120, the inversion layer at the interface between the support substrate 3010 and the BOX layer 3020 can become depleted. Accordingly, a parasitic interaction between the first and second MOS capacitors 3110 a, 3110 b can decrease, and a Q-factor of a variable capacitor array including the first and second MOS capacitors 3110 a, 3110 b can increase.

In one embodiment, the substrate bias circuit 3120 is used to control the voltage level of the support substrate 3010 to a voltage level in the range of about 10 V to about 40 V. However, other voltage levels are possible, including, for example, voltage levels associated with a particular fabrication process.

Although FIG. 22 illustrates an IC fabricated using an SOI process, the teachings herein are applicable to ICs fabricated using any of a wide range of processing technologies, including, for example, CMOS processes.

FIG. 23A is a cross section of a MOS capacitor 3500 according to one embodiment. The MOS capacitor 3500 includes source and drain regions 3510 a, 3510 b, respectively, which collectively operate as the MOS capacitor's cathode. The MOS capacitor 3500 further includes a gate region 3530, which operates as the MOS capacitor's anode.

As shown in FIG. 23A, the source and drain regions 3510 a, 3510 b are disposed in the device layer 3030. Additionally, the device layer 3030 is disposed over the BOX layer 3020, which in turn is disposed over the support substrate 3010. Additionally, the gate oxide region 3520 is disposed over the device layer 3030, and the gate region 3530 is disposed over the gate oxide region 3520.

The illustrated MOS capacitor 3500 includes a first halo or pocket implant 3550 a and a second halo or pocket implant 3550 b. Certain manufacturing processes include halo implantation to control transistor performance for relatively small gate lengths, such as gate lengths of 50 nm or less. For instance, halo implants can be used to limit an amount of diffusion of source and/or drain regions underneath edges of a gate during high temperature processes associated with semiconductor fabrication. Absent inclusion of halo implants, source and drain regions may diffuse unduly close to one another. For example, the source and drain regions may diffuse to provide a relatively short channel length that is susceptible to punch through at low drain to source voltage (VDS) voltage levels.

The halo implants can include a doping polarity that is opposite that of active regions associated with source and drain regions. For example, when active regions associated with source and drain regions are n type, the halo implants can be p type. Additionally, when active regions associated with source and drain regions are p type, the halo implants can be n type.

FIG. 23B is a cross section of a MOS capacitor 3600 according to another embodiment. The MOS capacitor 3600 of FIG. 23B is similar to the MOS capacitor 3500 of FIG. 23A, except that the MOS capacitor 3600 omits the first and second halo regions 3550 a, 3550 b of FIG. 23A.

Configuring the MOS capacitor 3600 in this manner can result in a relatively large amount of diffusion of the source and drain regions 3510 a, 3510 b. However, in the illustrated configuration, the source and drain regions 3510 a, 3510 b are electrically connected to one another and operate as a cathode. Thus, the MOS capacitor 3600 can remain operable even when the source and drain regions 3510 a, 3510 b diffuse relatively close to one another and/or diffuse into one another.

In certain embodiments, a MOS capacitor fabricated without halo or pocket implants can exhibit higher Q-factor and/or smaller capacitance variation in the presence of RF signals relative to a configuration in which the pocket implants are included.

Although FIGS. 23A and 23B illustrate MOS capacitors in context of an SOI process, the teachings herein are applicable to MOS capacitors fabricated using a wide range of processing technologies, including, for example, CMOS processes.

Terms such as above, below, over and so on as used herein refer to a device orientated as shown in the figures and should be construed accordingly. It should also be appreciated that because regions within a semiconductor device are defined by doping different parts of a semiconductor material with differing impurities or differing concentrations of impurities, discrete physical boundaries between different regions may not actually exist in the completed device but instead regions may transition from one to another. Some boundaries as shown in the accompanying figures are of this type and are illustrated as abrupt structures merely for the assistance of the reader. In the embodiments described above, p-type regions can include a p-type semiconductor material, such as boron, as a dopant. Further, n-type regions can include an n-type semiconductor material, such as phosphorous, as a dopant. A skilled artisan will appreciate various concentrations of dopants in regions described above.

CONCLUSION

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Likewise, the word “connected”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

Moreover, conditional language used herein, such as, among others, “can,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.

The above detailed description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are presented in a given order, alternative embodiments may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to other systems, not only the system described above. The elements and acts of the various embodiments described above can be combined to provide further embodiments.

While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure. 

What is claimed is:
 1. A capacitor structure comprising: a substrate; a source/drain region formed in said substrate to form an active area having an active area width, said source/drain region having a reflection symmetry; and a plurality of gates formed above said substrate, each of said plurality of gates having a gate width, said gate width configured to be less than said active area width, and said plurality of gates formed to have reflection symmetry.
 2. The capacitor structure of claim 1, wherein said substrate is an silicon-on-insulator substrate.
 3. The capacitor structure of claim 1, wherein said plurality of source/drain regions, and said plurality of gates are interconnected to form one or more pairs of capacitors connected in an anti-series configuration.
 4. The capacitor structure of claim 1, wherein said plurality of source/drain regions, and said plurality of gates are interconnected to form a variable capacitor cell of a variable capacitor array.
 5. The capacitor structure of claim 4, wherein the variable capacitor cell is part of an integrated circuit.
 6. The capacitor structure of claim 1, wherein said plurality of source/drain regions, and said plurality of gates are interconnected to form a plurality of variable capacitor cells of a variable capacitor array.
 7. A method to form a plurality of capacitors comprising: forming a source/drain region in a substrate to form an active area having an active area width, said source/drain region having reflection symmetry; and forming a plurality of gates above said substrate, each of said plurality of gates having a gate width, said gate width configured to be less than said active area width, and said plurality of gates formed to have reflection symmetry.
 8. The method of claim 7, wherein said substrate is an silicon-on-insulator substrate.
 9. The method of claim 7, further comprising forming connections between said plurality of source/drain regions, and said plurality of gates to form one or more pairs of capacitors connected in an anti-series configuration.
 10. The method of claim 7, further comprising forming connections between said plurality of source/drain regions, and said plurality of gates to form a variable capacitor cell of a variable capacitor array.
 11. The capacitor structure of claim 7, further comprising forming connections between said plurality of source/drain regions, and said plurality of gates to form a plurality of variable capacitor cells of a variable capacitor array.
 12. An integrated circuit comprising: a substrate; a source/drain region formed in said substrate to form an active area having an active area width, said source/drain region having an active area width; and a plurality of gates formed above said substrate, each of said plurality of gates having a gate width, said gate width configured to be less than said active area width, and said plurality of gates formed to have reflection symmetry.
 13. The integrated circuit of claim 12, wherein said substrate is a silicon-on-insulator substrate.
 14. The integrated circuit of claim 12, wherein said plurality of source/drain regions, and said plurality of gates are interconnected to form one or more pairs of capacitors connected in an anti-series configuration.
 15. The integrated circuit of claim 12, wherein said plurality of source/drain regions, and said plurality of gates are interconnected to form a variable capacitor cell of a variable capacitor array.
 16. The integrated circuit of claim 12, wherein said plurality of source/drain regions, and said plurality of gates are interconnected to form a plurality of variable capacitor cells of a variable capacitor array.
 17. The integrated circuit of claim 12, further comprising a bias voltage generator configured to generate a bias voltage for each one of said plurality of variable capacitor cells of said variable capacitor array.
 18. The integrated circuit of claim 17, further comprising an interface configured to receive a control signal for said bias voltage generator used to adjust a value of said bias voltage for each one of said plurality of variable capacitor cells of said variable capacitor array.
 19. The integrated circuit of claim 18, wherein said interface is a Mobile Industry Processor Interface radio front end interface.
 20. The integrated circuit of claim 12, wherein said plurality of source/drain regions, and said plurality of gates are interconnected to form a plurality of variable capacitor arrays. 